1. Field of Invention
The present invention relates generally to methods and means for evaluating body tremors so as to distinguish tremors due to pathological conditions from non-pathological conditions.
2. Background of Related Art
Monitoring the physiological body tremor of humans or animals is an attractive idea as far as the neurological pathologies are concerned. A method which is non-invasive and relatively easy to perform for screening and detection of disorders at an early stage of development is desirable.
Different types of human body tremor result from a variety of mechanisms that include peripheral and central loops and central oscillators. In general, the sources of tremor may be classified as mechanical, reflex and central oscillator (Hallet, 1998)1. The mechanical tremor results from the inertial and stiffness characteristics of the human joints, whereas the reflex tremor originates from the peripheral and central reflex loops of the nervous system. The central regions of the nervous system may undergo spontaneous oscillations and send out rhythmic motor commands, which could lead to physiological termor of the human body.
Abnormalities in the physiological tremor may appear due to different pathologies of the nervous system. Essential tremor results from a central oscillator and has a frequency range of 8-12 Hz. Several types of tremors can be observed in patients with Parkinson's disease, but the most characteristic one is the tremor that is present at rest. It has a characteristic frequency between 3-7 Hz. Other very common types of tremor are the cerebellar, palatal, orthostatic, neuropathic and cortical tremors.
Several studies analyzed tremor in different parts of the body. Wade et al (1982)2 measured tremor of the hand by placing an accelerometer on the dorsum of the hand. Amplitude and spectral characteristics of hand tremor were evaluated. In another study, Gallasch and Kenner (1997)3 investigated the microvibration of the arm recorded with an accelerometer. The analysis was carried out during resting of the arm and gripping actions.
The measurement of the microvibrations of the body using a force plate date back to mid 70's. Bircher et al. (1978)4 examined the effect of examination stress on the microvibrations of the human body that is quantified by measuring the rectified impulse using a force plate. The study also established a correlation between the vertical force during standing and cardiac output. In a different study, Seliktar et al. (1978)5 tried to classify three different components of the ground reaction force during standing. A relatively higher frequency component was termed as “tremor” whereas an intermediate frequency component was designated as “ataxia”. The lowest frequency constituent was labeled as “sway”. Three different groups of subjects were tested: a control group, a group of patients with hemiplegia and a group of patients after severe cranio-cerebral injury. In a similar study, Strum et al. (1980)6 evaluated the relationship between the cardiac activity and the microvibrations of the body. A force plate was used to assess the influence of the cardiac activity and muscle tone on the microvibrations under different test conditions. The effect of isoprenaline, exercise, cold stress and trunk flexion on microvibration was measured and compared to control subjects. The main conclusion was that the most important source of whole-body microvibration is the cardiac activity. Koller et al. (1986)7 evaluated the effect of propranolol on whole-body microvibrations during examination stress. Similar to previous studies, the rectified impulse calculated using force plate data was used to assess microvibrations.
Prior to the present invention, the methods used to identify different types of body tremors required special equipment to be used such as exemplified in U.S. Pat. Nos. 4,595,023 and 5,265,619. A method using standard and readily commercially available components to measure and quantify body tremor would represent a significant advance over prior methods.